The present invention relates to magnetic storage systems. More specifically, the present invention relates to magnetoresistive sensors used in magnetic storage systems to read back stored information.
Magnetic storage systems are used to store information in a magnetic format for subsequent retrieval. Various technologies are available for reading back the stored information. One promising technology is the use of a magnetoresistive sensor for such read back.
Magnetoresistive sensors are responsive to a change in resistivity caused by the presence of magnetic fields and are increasingly being employed as read back elements in the heads of magnetic disc drives. They are particularly advantageous because the change in resistivity is independent of disc speed and depends only on the magnetic flux. Further, the sensor output is easily scaled by adjusting the sense current.
Magnetoresistive sensors typically comprise a thin strip of ferromagnetic material such as NiFe magnetized along an easy axis of low coercivity. The strip is mounted in the head such that the easy axis is transverse to the direction of disc rotation and parallel to the plane of the disc. Magnetic flux from the disc surface causes rotation of the magnetization vector of the stip, which in turn causes a change in electrical resistivity. A sense current is passed through the thin strip and the magnetic flux can be detected by measuring the change in voltage across the element as a result of the changing resistivity.
One drawback with magnetoresistive sensors is that the resistance of the magnetoresistive element and its sensitivity vary with temperature. Magnetoresistive sensor parametrics have been measured to degrade at ambient temperatures as low as 65.degree. C. However, during operation of the magnetoresistive sensor, its temperature tends to rise due, to for example, current flowing through the sense element, and the general increase in the ambient temperature from other components in the disc drive system such as the spindle motor, actuator and control circuitry. Common operating temperatures are as high as 60.degree. C. during normal operation, or even higher during intense operation. Further, the ambient temperature for high end components is being pushed higher as higher speeds, increased seek rates, and higher density components are designed. The prior art has focused on making the magnetoresistive sensor element less heat sensitive and/or attempting to compensate for this temperature dependency.